I have a theory about dark matter:
The double-slit experiment says that elementary particles can behave as both particles and waves. I've never been able to fully accept that. It means that a particle turns into a wave and then recombines to become a particle.
However... what if dark matter was a fluid that permeated the universe. All particles vibrate due to their energy. If you drop a rock into a pond it creates waves. In the same way if you shoot a particle into a fluid it will create waves.
So the particle is moving from the emitter towards the slits. There's a wave in front of it. The wavefront bounces off the solid area and also goes through the slits. This creates an interference pattern. The interference pattern is a complex wave with high and low pressure zones. The particle will follow the path of least resistance. Sometimes it will strike the plate. Sometimes it will go through the left slit and sometimes through the right.
So, yes, there's still wave-particle duality but it's because there's a wave around the particle. The particle is always a single particle and is never in two places at the same time. It's wavefront, however, is affected by the surrounding and dictates the path the particle will take. The path is randomized due to various factors so sometimes the path of least resistance is the left slit and sometimes it's the right slit. The wavefront behind the slits has all sort of peaks and nulls due to interference and the particle follows the troughs.
Therefore what I'm thinking is that wave-particle duality is actually due to a dark matter fluid that creates waves around particles.
It also explains the patterns with a single slit. The wavefront passes through the slit and there is diffraction off the edges of the slit. This causes lobing of the wavefront. Sometimes the particle will follow a sidelobe path due to random fluctuations.
IOW, there's a wave that propagates through the fluid and the particle follows the troughs in the wave.